1. Field of the Invention
The present invention relates to an ultrasonic motor comprising a stator including a bending vibration plate, a longitudinal and torsional vibration coupling element having a beam extending slated relative to the vibration axis of the bending vibration plate, a piezoelectric thickness vibration element connected with the longitudinal and torsional vibration coupling element through an elastic vibration element, a longitudinal vibration element combined with the longitudinal and torsional vibration coupling element, the elastic vibration element and the piezoelectric thickness vibration element, said beam of the stator generating elliptical vibration which is combination of longitudinal vibration generated in the piezoelectric thickness vibration elements and then boosted in the elastic vibration element and torsional vibration generated in the longitudinal and torsional vibration coupling element excited by the longitudinal vibration and therefore having the same frequency of the vertical vibration, and a rotor which is contacted with the leg of the stator to receive the elliptical vibration to be rotated.
2. Description of the Prior Art
The conventional ultrasonic motor is comprised of a vertical vibration element such as a bolt fasten vibrator which has been used in the ultrasonic industry. However in order to rotate a rotor, the vertical vibration has to be transformed into a rotational torque and therefore, many problems occur. In order to generate the rotational torque, ultrasonic elliptical vibration should be used. However, there has not been available an ultrasonic vibration element which can directly generate elliptical vibrations. Thus, it can not be expected to manufacture ultrasonic motor using ultrasonic elliptical vibration element. Piezoelectric motors using the elliptical vibration of the traveling elastic wave have a problem that the input and output efficiency is low.
As a result of a study attempting to solve the problems mentioned above, an ultrasonic motor having a stator using the ultrasonic elliptical vibration element in a cantilever manner was developed, but the motor has not shown sufficient desirable results.
The ultrasonic vibration element in the cantilever manner thus developed is shown in FIG. 8(a), in which a rotational torque can be obtained on a rotor pressed onto a free surface of the beam 1b by generation of the elliptical vibration 31 having one diameter in a direction perpendicular to the free surface of the beam 1b. The elliptical vibration can be generated by combining a tosional vibration 25 based on a bending vibration 26 of the bending vibration plate 1a integrally formed with the beam 1b and a vertical vibration having the same frequency of a vibration driving the bending vibration plate 1a. The bending vibration of the bending vibration plate 1a is transformed into the torsion 26 because the longitudinal direction of the bending vibration plate 1a is slanted relative to the center line X--X of the bending vibration as shown in FIG. 8b. In order to generate the elliptical vibration on the free end surface of a cantilever element, it is essential to arrange the beam 1b against the center line X--X of the bending vibration of the bending vibration plate 1a. However, when such a construction is adopted, the direction of the torsion acting on the beam 1b can not be perpendicular to the longitudinal direction of the beam 1b, whereby there occurs a component displaced from the direction perpendicular to the longitudinal direction.
In the ultrasonic motor using the vibration element mentioned above as the stator to which a rotor is rotatably depressed, the vectors of the rotational torque are shown at 28 and 28' in FIG. 8b. As understood, there occur vector components 29 and 29' in a radius direction of the rotor other than the vector components 27 and 27' of the tangent of the circumference of the rotor. The torque of the radius direction causes the depressing surface of the stator to rub the rotor surface in the radius direction. Apparently this rubbing motion does not contribute to an increase in the rotational torque of the rotor but wears off the surfaces of the stator and the rotor. In order to provide the torsional vibration of the rotor, it is necessary to make the beam slanted relative to the center line of the bending vibration, however such a slanted beam causes a force in the radial direction.